GAMMA DEVICES — stationary installations for radiation therapy and experimental radiation which basic element is the radiation head with a source of gamma radiation.
G.'s development - and. began practically since 1950. As a source of radiation used radium in the beginning ( 226 Ra); afterwards it was replaced with cobalt ( 60 With) and caesium ( 137 Cs). In the course of improvement devices GUT-So-20, GUT-So-400, Tungsten, the Beam, ROKUS, RAD and then dalnedistantsionny AGAT-S, AGAT-R, ROKUS-M, etc. were designed. G.'s improvement - and. goes on the way of creation of devices with program control by a session of radiation: management of movement of a source of radiation, automatic reproduction of earlier programmed sessions, radiation in the set parameters of the dozny field and results of anatomo-topographical inspection of the patient.
- and. are intended preferential for treatment of patients with malignant tumors (see. Gamma therapy ), and also for pilot studies (experimental gamma irradiators).
Therapeutic gamma devices consist of a support, the radiation head strengthened on it with a source of ionizing radiation and a table manipulator, on Krom the patient accommodates.
The radiation head is made of heavy metal (lead, tungsten, uranium) which is effectively weakening gamma radiation. For overlapping of a bunch of radiation the lock or the conveyor moving a source of radiation from the provision of radiation to the provision of storage is provided in a design of a radiation head. At radiation the source of gamma radiation is established opposite to the opening in protection material serving for an exit of a bunch of radiation. In a radiation head there is a diaphragm intended for formation of an external contour of the field of radiation and auxiliary elements — trellised diaphragms, the wedge-shaped and compensating filters and shadow blocks serving for formation of a bunch of radiation and also the device for aiming of a bunch of radiation at an object — a centralizer (localizer).
The design of a support provides distance steering with a bunch of radiation. Depending on a design of a support distinguish G. - the ampere-second a motionless bunch of radiation intended for static radiation and also radiations, rotational and rotational and convergent with a mobile bunch (fig. 1 — 3). Devices with a mobile bunch of radiation allow to lower beam load of skin and the subject healthy fabrics and to concentrate a maximum of a dose in a tumor. According to a technique of treatment of G. - and. divide on dalnedistantsionny, close remote and devices for an intracavitary gamma therapy.
Use devices of ROKUS-M, AGAT-R and AGAT-S with radiation activity from 800 to several thousand curies to radiation of the tumors located at a depth of 10 cm and more. Devices with high activity of the source of radiation located at considerable distance from the center of a tumor (60 — 75 cm) provide high concentration of a dose of radiation in a tumor (e.g., at a depth of 10 cm the dose of radiation makes 55 — 60% of superficial) and the big power of an air dose of radiation (60-4-90 P/mines at distance 1 from a source) that allows to reduce a radiation time to several minutes.
For radiation of the tumors located at a depth of 2 — 5 cm use blizkodistantsionny G. - and. (RITS) which activity of a source of radiation does not exceed 200 curies; radiation carry out 5 — 15 cm at distance.
For intracavitary radiation in gynecology and a proctology use the special device AGAT-V (fig. 4). The radiation head of this device contains seven sources of radiation the general activity of 1 — 5 curie. The device is supplied a set of endostat for introduction to a cavity and the station of airsupply with the hoses providing pneumatic delivery of sources from a radiation head in endostata.
The room intended for carrying out a gamma therapy usually is located on the first floor or in a semi-basement of an angular part of the building, outside on perimeter fenced off by a protective belt 5 m wide (see. Radiological department ). In it is available one or two procedural halls of 30 in size — 42 m 2 , 3,0 high — 3,5m. The procedural hall is partitioned on 2/3 — 3/4 in width by a protective wall. Management G. - and. and overseeing by the patient in the course of radiation is conducted from the console room through a glory-hole with lead or tungsten glass with a density of 3,2 — 6,6 g/cm 3 or on TV what guarantees full radiation safety of medical staff. Console and the procedural hall are connected by the intercom. The door to the procedural hall is upholstered with sheet lead. There is also a room for the electric starting equipment and devices of food for G. - and. the ROKUS type, the room for the air-ventilation chamber (ventilation of procedural and console shall provide 10-fold exchange of air within 1 hour), dosimetric laboratory, in a cut devices and devices for dosimetric researches by preparation of the plan of beam treatment (dosimeters, izodozograf) are placed, devices for obtaining anatomo-topographical data (konturometra, tomographs, etc.); the equipment providing orientation of a bunch of radiation (optical and x-ray centralizers, simulators of a gamma-ray beam); devices for control of observance of the plan of radiation.
Experimental gamma irradiators (EGO; isotope gamma-ray irradiation plants) are intended for beam impact on various objects for the purpose of studying of action of ionizing radiation. EGOS widely apply in a radiochemistry and radiobiology, and also for the purpose of studying of questions of practical use of gamma-ray irradiation plants to radiation of page - x. products and «cold» sterilization of various objects in the food and medical industry.
EGOS, as a rule, represent the stationary installations supplied with special devices for protection against not used radiation. As protection materials apply lead, cast iron, concrete, water, etc.
The experimental gamma-ray irradiation plant usually consists of the camera, in to-ruyu the irradiated object, the storage for sources of radiation supplied with the mechanism for management of a source, and system of the blocking and signaling devices excluding a possibility of hit of personnel in an exposure cell at the included irradiator is located. The exposure cell is usually produced from concrete. An object is entered into the camera through a labyrinth entrance or through the apertures blocked by thick metal doors. Near the camera or in the camera there is a storage for a source of radiation in the form of the pool with water or a special protective container. In the first case the source of radiation is stored at a dock apron at a depth of 3 — 4 m, in the second — in a container. The source of radiation is moved from storage to an exposure cell by means of electromechanical, hydraulic or pneumatic pressure drives. Also so-called self-protective installations combining in one protective block an exposure cell and storage for a source of radiation are used. In these installations the source of radiation is not mobile; the irradiated objects deliver to it via special devices like locks.
A source of gamma radiation — usually drugs of a telecobalt or caesium — place in the irradiators of various form (depending on purpose of installation) providing uniformity of radiation of an object and high dosage rate of radiation. Activity of a source of radiation in gamma irradiators can be various. In pilot units it reaches several tens of thousands curie, in powerful plants — to several million curies. The size of activity of a source determines the major parameters of the unit: power of beam influence, its capacity and thickness of protective barriers.
See also Gamma radiation .
Bibliography: Bibergal A. V., Sinitsyn V. I. ileshchinskiyn. I. Isotope gamma-ray irradiation plants, M., 1960; Galina L. S., etc. Atlas of dozny distributions, Multifield and rotational radiation, M., 1970; Kozlova A. V. Radiation therapy of malignant tumors, M., 1971, bibliogr.; To about N d r ash about in V. M., Yemelyanov V. T. and Sulkin A. G. Stol for a gammatera-piya, Medical radio-gramophones., t. 14, No. 6, page 49, 1969, bibliogr.; Ratner T. G. and Bibergal A. V. Formation of dozny fields at remote gamma therapy, M., 1972, bibliogr.; P and m of m and A. F. N, etc. Experimental hose v-terapev-tichesky the device for intracavitary radiation in book: Radiatsion. tekhn., under the editorship of A. S. Shtan, century 6, page 167, M., 1971, bibliogr.; Sulkin A. G. and Zhukovsky E. A. Rotational gamma and therapeutic device, Atomn. energy, t. 27, century 4, page 370, 1969; Sulkin A. G. and P and m of m and A. F N. Radio isotope therapeutic devices for tele-irradiation, in book: Radiatsion. tekhn., under the editorship of A. S. Shtan, century 1, page 28, M., 1967, bibliogr.; Tumanyan M. A. and To and at sh and N with to and y D. A. Radiation sterilization, M., 1974, bibliogr.; Tyubiana M. of ides of river. Physical bases of radiation therapy and radiobiology, the lane with fr., M., 1969.
E. A. Zhukovsky, I. K. Tabarovsky